1. Field of the Invention
The present invention relates to a lanthanum gallate-based sintered body and a solid oxide fuel cell using the same as a solid electrolyte. More specifically, the present invention relates to a sintered body containing lanthanum gallate-based oxide that is perovskite-type ceramics as a base material, and to a solid oxide fuel cell using the same as a solid electrolyte.
2. Description of the Related Art
A solid oxide fuel cell (hereinafter, also described as “SOFC”) has continued to progress since a solid electrolyte was discovered by Nernst in 1899 and the SOFC was operated by Baur and Preis in 1937.
The SOFC is usually operated at a high temperature of 1000° C. or more, and such a high operation temperature greatly narrows the range of selectable materials for composing the cell. For example, it becomes difficult to use metallic parts for a cell container. Accordingly, a development of solid electrolyte materials having high oxygen-ion conductivity even at a low temperature is desired.
As such solid electrolyte materials, stabilized zirconia, stabilized bismuth, a ceria-based material, perovskite-type ceramics and the like, which use stabilizers such as oxides of alkaline-earth elements (CaO, MgO, Sc2O3 and the like) and rare-earth oxides (Y2O3 and the like) are known. Among them, a sintered body containing, as a base material, lanthanum gallate-based oxide as one of perovskite-type ceramics has attracted attention in recent years because this sintered body can have relatively high oxygen-ion conductivity even at a low temperature range.
However, the sintered body containing the lanthanum gallate-based oxide as the base material is low in mechanical strength, and therefore, a sufficient mechanical strength must be ensured by thickening the solid electrolyte. However, the thickening of the solid electrolyte will increase the resistance of the solid electrolyte itself in the SOFC.
Accordingly, an improvement of the mechanical strength of the lanthanum gallate-based oxide has been attempted. For example, there has been disclosed a technology of adding alumina powder (Al2O3) for the purpose of improving the mechanical strength of the sintered body containing the lanthanum gallate-based oxide as the base material (refer to Japanese Patent Application Laid-open No. 2000-44340).